In U.S. Pat. No. 3,128,640, a torsion damper of the kind generally called a coaxial or concentric torsion damper is described. In that damper, the torque is transmitted from a disc to a pair of rings known as guide rings, by means of a first spring damping device, the torque being transmitted from the guide rings to a damper or hub plate through a second spring damping device.
The friction associated with the damper plate is controlled by means of spacers which connect the guide rings to each other and pass through passage means formed in the disc.
The friction between the disc and the damper plate is controlled through the thickness of the damper plate by means of plates fixed to the disc and connected to each other by riveting.
Because of he localisation of the spacers at the outer periphery of the guide rings, such an arrangement leads to some deformation of the guide rings. The length of the guide rings is considerable, such that, being weakened at their outer periphery by the spacers, they have a tendency when in contact with the damper plate to move apart or spread at their inner periphery, which is detrimental to the friction effect.
In addition, the spacers and the rivets are generally disposed all on the same pitch circle as the openings which are formed in the disc for accommodating the springs. As a result, and with particular relevance to the question of mechanical strength of the disc, the spacing between the two damping devices cannot be made as large as is desirable.